Apparatus and methods for envelope tracking in a mobile device

ABSTRACT

Apparatus and methods for envelope tracking in a mobile device are disclosed herein. In certain configurations, a method includes amplifying a radio frequency (RF) input signal using a power amplifier, providing power to the power amplifier from a power amplifier supply voltage, controlling a voltage level of the power amplifier supply voltage based on a control voltage using a DC-to-DC converter, adjusting the voltage level of the power amplifier supply voltage based on an envelope of the RF input signal using an error amplifier, low pass filtering the power amplifier supply voltage to generate a filtered voltage using a low pass filter, and generating the control voltage based on comparing the filtered voltage to a reference voltage using a comparator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/640,917, filed Mar. 6, 2015 and titled “APPARATUS AND METHODS FORENVELOPE TRACKERS,” which is a continuation of U.S. patent applicationSer. No. 13/763,380, filed Feb. 8, 2013 and titled “APPARATUS ANDMETHODS FOR ENVELOPE TRACKING,” which claims the benefit of priorityunder 35 U.S.C. §119(e) of U.S. Provisional Patent Application No.61/597,048, filed Feb. 9, 2012 and entitled “APPARATUS AND METHODS FORENVELOPE TRACKING,” and of U.S. Provisional Patent Application No.61/658,714, filed Jun. 12, 2012 and entitled “APPARATUS AND METHODS FORENVELOPE TRACKING,” each of which are herein incorporated by referencein their entireties.

BACKGROUND

1. Field

Embodiments of the invention relate to electronic systems, and inparticular, to envelope tracking systems for radio frequency (RF)electronics.

2. Description of the Related Technology

Power amplifiers can be included in mobile devices to amplify an RFsignal for transmission via an antenna. For example, in mobile deviceshaving a time division multiple access (TDMA) architecture, such asthose found in Global System for Mobile Communications (GSM), codedivision multiple access (CDMA), and wideband code division multipleaccess (W-CDMA) systems, a power amplifier can be used to amplify an RFsignal having a relatively low power. It can be important to manage RFsignal amplification, as a desired transmit power level can depend onhow far the user is away from a base station and/or the mobileenvironment. Power amplifiers can also be employed to aid in regulatingthe power level of the RF signal over time, so as to prevent signalinterference from transmission during an assigned receive time slot.

The power consumption of a power amplifier can be an importantconsideration. One technique for reducing power consumption of a poweramplifier is envelope tracking, in which a supply voltage of the poweramplifier is controlled in relation to the envelope of the RF signal orsignal envelope. Thus, when a voltage level of the signal envelopeincreases the voltage level of the power amplifier supply voltage can beincreased. Likewise, when the voltage level of the signal envelopedecreases the voltage level of the power amplifier supply voltage can bedecreased to reduce power consumption.

There is a need for improved power amplifier systems. Furthermore, thereis a need for improved envelope trackers.

SUMMARY

In certain embodiments, the present disclosure relates to a mobiledevice. The mobile device includes a power amplifier, a buck converter,and an error amplifier. The power amplifier is configured to receive apower amplifier supply voltage and to amplify a radio frequency (RF)input signal to generate an RF output signal. The buck converter isconfigured to convert a battery voltage into a buck voltage, and tocontrol a magnitude of the buck voltage based on an error current. Theerror amplifier is configured to generate an output current based on anenvelope of the RF input signal and to generate the power amplifiersupply voltage by adjusting the magnitude of the buck voltage using theoutput current. The error amplifier is configured to control the buckconverter by changing a magnitude of the error current in relation to amagnitude of the output current.

In various embodiments, the mobile device further includes an ACcoupling capacitor electrically connected between the power amplifiersupply voltage and an output of the error amplifier configured togenerate the output current.

In some embodiments, the buck converter includes a buck controller, abuck inductor and a plurality of buck switches, and the buck controlleris configured to use the error current to control a state of theplurality of buck switches so as to control a current through the buckinductor.

In a number of embodiments, the error current includes a non-invertederror current component and an inverted error current component, and thebuck converter includes a current comparator configured to control thestate of the plurality of buck switches by comparing the non invertederror current component to the inverted error current component.

In accordance with several embodiments, the error amplifier includes afirst pair of transistors configured to generate the output current anda second pair of transistors configured to generate the error current,and the second pair of transistors are implemented as a replica of thefirst pair of transistors.

In some embodiments, the mobile device further includes an antennaconfigured to receive the RF output signal.

In a number of embodiments, the mobile device further includes atransceiver configured to generate the envelope of the RF input signal.

In certain embodiments, the mobile device further includes a batteryconfigured to generate the battery voltage.

In several embodiments, the error amplifier is powered using the batteryvoltage.

In some embodiments, the mobile device further includes a boostconverter configured to convert the battery voltage into a boost voltagehaving a voltage magnitude greater than a voltage magnitude of thebattery voltage. The error amplifier is powered using the boost voltage.

In certain embodiments, the present disclosure relates to an envelopetracker for generating a power amplifier supply voltage. The envelopetracker includes a buck converter and an error amplifier. The buckconverter is configured to convert a battery voltage into a buckvoltage, and to control a magnitude of the buck voltage based on anerror current. The error amplifier is configured to generate an outputcurrent based on an envelope signal and to generate the power amplifiersupply voltage by adjusting the magnitude of the buck voltage using theoutput current. The error amplifier is configured to control the buckconverter by changing a magnitude of the error current in relation to amagnitude of the output current.

In accordance with a number of embodiments, the error amplifier includesa first input configured to receive the envelope signal, a second input,and an output configured to generate the output current. In someembodiments, the envelope tracker further includes a feedback circuitelectrically connected between the second input of the error amplifierand the output of the error amplifier. In a number of embodiments, theenvelope tracker further includes an AC coupling capacitor disposedbetween the output of the error amplifier and the power amplifier supplyvoltage.

In certain embodiments, the error amplifier is powered using the batteryvoltage.

According to several embodiments, the envelope tracker further includesa boost converter configured to convert the battery voltage into a boostvoltage having a voltage magnitude greater than a voltage magnitude ofthe battery voltage. The error amplifier is powered using the boostvoltage.

In various embodiments, the buck converter includes a buck controller, abuck inductor and a plurality of buck switches. The buck controller isconfigured to use the error current to control a state of the pluralityof buck switches so as to control a current through the buck inductor.

In a number of embodiments, the error current includes a non-invertederror current component and an inverted error current component, and thebuck converter includes a current comparator configured to control thestate of the plurality of buck switches by comparing the non invertederror current component to the inverted error current component.

In some embodiments, the error amplifier includes a first pair oftransistors configured to generate the output current and a second pairof transistors configured to generate the error current, and the secondpair of transistors are implemented as a replica of the first pair oftransistors. In various embodiments, the first pair of transistorsincludes a first p type field effect transistor (PFET) and a first ntype field effect transistor (NFET) and the second pair of transistorsincludes a second PFET and a second NFET.

In certain embodiments, the present disclosure relates to a method ofgenerating a power amplifier supply voltage. The method includesgenerating a buck voltage from a battery voltage using a buck converter,controlling a magnitude of the buck voltage based on an error current,generating an output current based on an envelope signal using an erroramplifier, generating the power amplifier supply voltage by adjustingthe magnitude of the buck voltage using the output current, andcontrolling the buck converter by changing a magnitude of the errorcurrent in relation to a magnitude of the output current.

In various embodiments, the buck converter includes a buck inductor anda plurality of buck switches, and the method further includescontrolling a current through the buck inductor by controlling a stateof the plurality of buck switches based on the error current.

In some embodiments, the error current includes a non-inverted errorcurrent component and an inverted error current component, and themethod further includes controlling the state of the plurality of buckswitches by comparing the non-inverted error current component to theinverted error current component.

In certain embodiments, the method further includes providing the poweramplifier supply voltage to a power amplifier.

According to a number of embodiments, the method further includespowering the error amplifier using the battery voltage.

In various embodiments, the method further includes generating a boostvoltage using a boost converter and powering the error amplifier usingthe boost voltage.

In certain embodiments, the present disclosure relates a multi-chipmodule (MCM). The MCM includes a buck converter and an error amplifier.The buck converter is configured to convert a battery voltage into abuck voltage, and to control a magnitude of the buck voltage based on anerror current. The error amplifier is configured to generate an outputcurrent based on an envelope signal and to generate the power amplifiersupply voltage by adjusting the magnitude of the buck voltage using theoutput current. The error amplifier is configured to control the buckconverter by changing a magnitude of the error current in relation to amagnitude of the output current.

In various embodiments, the error amplifier includes a first inputconfigured to receive the envelope signal, a second input, and an outputconfigured to generate the power amplifier supply voltage. According tosome embodiments, the MCM further includes a feedback circuitelectrically connected between the second input of the error amplifierand the output of the error amplifier. In certain embodiments, the MCMfurther includes an AC coupling capacitor disposed between the output ofthe error amplifier and the power amplifier supply voltage.

In some embodiments, the MCM further includes a power amplifierconfigured to receive the power amplifier supply voltage.

In certain embodiments, the present disclosure relates to an envelopetracking system for generating a power amplifier supply voltage. Theenvelope tracking system includes a DC-to-DC converter and an erroramplifier. The DC-to-DC converter is configured to generate a regulatedvoltage from a battery voltage, and to control a voltage magnitude ofthe regulated voltage using a low frequency feedback signal that isbased on a low frequency component of the power amplifier supplyvoltage. The error amplifier is configured to generate an output currentusing an envelope signal and a high frequency feedback signal that isbased on a high frequency component of the power amplifier supplyvoltage. Additionally, the error amplifier is configured to generate thepower amplifier supply voltage by adjusting the magnitude of theregulated voltage using the output current.

In various embodiments, the error amplifier includes a first inputconfigured to receive the envelope signal, a second input configured toreceive the high frequency feedback signal, and an output configured togenerate the output current. According to some embodiments, the envelopetracking system further includes an AC coupling capacitor electricallyconnected between the output of the error amplifier and the poweramplifier supply voltage. According to certain embodiments, the envelopetracking system further includes a feedback circuit configured togenerate the high frequency feedback signal. In various embodiments, thefeedback circuit includes a first feedback resistor electricallyconnected between the output of the error amplifier and the second inputof the error amplifier and a second feedback resistor electricallyconnected between the second input of the error amplifier and a powerlow supply voltage.

In several embodiments, the error amplifier is powered using the batteryvoltage.

In accordance with certain embodiments, the envelope tracking systemfurther includes an inductor electrically connected between theregulated voltage and the power amplifier supply voltage.

In some embodiments, the DC-to-DC converter includes a buck converterconfigured to generate the regulated voltage.

In various embodiments, the envelope tracking system further includes alow pass filter configured to filter the power amplifier supply voltageto generate a filtered power amplifier supply voltage, and the lowfrequency feedback signal is based in part on the filtered poweramplifier supply voltage. According to some embodiments, the envelopetracking system further includes a comparator configured to generate thelow frequency feedback signal by comparing the filtered power amplifiersupply voltage to a reference voltage. In several embodiments, theenvelope tracking system further includes a reference voltage generatorconfigured to generate the reference voltage.

In a number of embodiments, the envelope tracking system furtherincludes a high pass filter configured to filter the power amplifiersupply voltage to generate a filtered power amplifier supply voltage. Inseveral embodiments, the envelope tracking system further includes acomparator configured to compare the filtered power amplifier supplyvoltage to the envelope signal to generate a high frequency envelopesignal, and the error amplifier includes a first input configured toreceive the high frequency envelope signal, a second input configured toreceive the high frequency feedback signal, and an output configured togenerate the output current.

In certain embodiments, the present disclosure relates to a wirelessdevice. The wireless device includes a power management integratedcircuit (PMIC) and a power amplifier module. The PMIC includes aDC-to-DC converter configured to generate a regulated voltage from abattery voltage, and to control a voltage level of the regulated voltagebased on a voltage level of a control voltage. The power amplifiermodule includes a power amplifier configured to amplify a radiofrequency (RF) signal and an error amplifier configured to generate anoutput current based on an envelope signal. The error amplifier isconfigured to generate a power amplifier supply voltage for the poweramplifier by adjusting the voltage level of the regulated voltage usingthe output current. The power amplifier module is configured to changethe voltage level of the control voltage based at least in part on thepower amplifier supply voltage.

According to several embodiments, the wireless device further includes atransceiver configured to generate the RF signal and the envelopesignal.

In some embodiments, the wireless device further includes a batteryconfigured to generate the battery voltage.

In a number of embodiments, the power amplifier module further includesan inductor electrically connected between the regulated voltage and thepower amplifier supply voltage.

In accordance with certain embodiments, the wireless device furtherincludes a feedback circuit configured to generate a feedback signalthat changes in response to a high frequency component of the poweramplifier supply voltage, and the error amplifier includes a first inputconfigured to receive the envelope signal, a second input configured toreceive the feedback signal, and an output configured to generate theoutput current. In several embodiments, the power amplifier modulefurther includes an AC coupling capacitor electrically connected betweenthe output of the error amplifier and the power amplifier supplyvoltage.

In various embodiments, the power amplifier module further includes alow pass filter configured to filter the power amplifier supply voltageto generate a filtered power amplifier supply voltage, and the controlvoltage is based at least on part on the filtered power amplifier supplyvoltage. In some embodiments, the power amplifier module furtherincludes a comparator configured to generate the control voltage bycomparing the filtered power amplifier supply voltage to a referencevoltage.

In certain embodiments, the present disclosure relates to a method ofgenerating a power amplifier supply voltage. The method includesgenerating a regulated voltage from a battery voltage using a DC-to-DCconverter, controlling a magnitude of the regulated voltage based on acontrol voltage, generating an output current based on an envelopesignal using an error amplifier, generating a power amplifier supplyvoltage for a power amplifier by adjusting the magnitude of theregulated voltage using the output current, and controlling the DC-to-DCconverter by changing a voltage level of the control voltage based atleast in part on the power amplifier supply voltage.

In a number of embodiments, the method further includes providing theoutput current to the power amplifier supply voltage thru an AC couplingcapacitor.

According to various embodiments, the method further includes generatinga high frequency feedback signal for the error amplifier using afeedback circuit, and the high frequency feedback signal is configuredto change in response to a high frequency component of the poweramplifier supply voltage.

In several embodiments, the method further includes powering the erroramplifier using the battery voltage.

According to various embodiments, the method further includes filteringthe power amplifier supply voltage to generate a filtered poweramplifier supply voltage using a low pass filter, and comparing thefiltered power amplifier supply voltage to a reference voltage togenerate the control voltage.

In certain embodiments, the present disclosure relates to a radiofrequency system. The radio frequency system includes a power managementintegrated circuit (PMIC), a first power amplifier module, and a secondpower amplifier module. The PMIC includes a DC-to-DC converterconfigured to generate a regulated voltage from a battery voltage, andto control a voltage level of the regulated voltage using a plurality ofcontrol voltages. The first power amplifier module includes a firstpower amplifier configured to amplify a first radio frequency (RF)signal and a first error amplifier configured to generate a first poweramplifier supply voltage for the first power amplifier by adjusting thevoltage level of the regulated voltage based on an envelope of the firstRF signal. The first power amplifier module is configured to change thevoltage level of a first control voltage of the plurality of controlvoltages when the first power amplifier is enabled based at least inpart on a voltage level of the first power amplifier supply voltage. Thesecond power amplifier module includes a second power amplifierconfigured to amplify a second RF signal and a second error amplifierconfigured to generate a second power amplifier supply voltage for thesecond power amplifier by adjusting the voltage level of the regulatedvoltage based on an envelope of the second RF signal. The second poweramplifier module is configured to change the voltage level of a secondcontrol voltage of the plurality of control voltages when the secondpower amplifier is enabled based at least in part on a voltage level ofthe second power amplifier supply voltage.

In various embodiments, the first power amplifier module includes afirst inductor electrically connected between the regulated voltage andthe first power amplifier supply voltage and the second power amplifiermodule includes a second inductor electrically connected between theregulated voltage and the second power amplifier supply voltage.

In some embodiments, the radio frequency system further includes a phoneboard, a first inductor, and a second inductor. The first inductor isdisposed on the phone board and electrically connected between theregulated voltage and the first power amplifier supply voltage. Thesecond inductor is disposed on the phone board and electricallyconnected between the regulated voltage and the second power amplifiersupply voltage.

According to several embodiments, the radio frequency system furtherincludes a third power amplifier module including a third poweramplifier configured to amplify a third RF signal and a third erroramplifier configured to generate a third power amplifier supply voltagefor the third power amplifier by adjusting the voltage level of theregulated voltage based on an envelope of the third RF signal. The thirdpower amplifier module is configured to change the voltage level of athird control voltage of the plurality of control voltages when thethird power amplifier is enabled based at least in part on a voltagelevel of the third power amplifier supply voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a power amplifier module for amplifyinga radio frequency (RF) signal.

FIG. 2 is a schematic block diagram of an example wireless device thatcan include one or more of the power amplifier modules of FIG. 1.

FIG. 3A is a schematic block diagram of one example of a power amplifiersystem including an envelope tracker.

FIG. 3B is a schematic block diagram of another example of a poweramplifier system including an envelope tracker.

FIGS. 4A-4B show two examples of power amplifier supply voltage versustime.

FIG. 5 is a schematic block diagram of one embodiment of an envelopetracking system.

FIG. 6 is a circuit diagram of one embodiment of a boost converter.

FIG. 7 is a circuit diagram of one embodiment of a buck converter.

FIG. 8 is a circuit diagram of one embodiment of a hysteretic currentcomparator.

FIG. 9 is a circuit diagram of one embodiment of an error amplifier.

FIG. 10 is a schematic block diagram of another embodiment of anenvelope tracking system.

FIG. 11 shows one example of a graph of current versus time for theenvelope tracking system of FIG. 5.

FIG. 12 is a schematic block diagram of another embodiment of anenvelope tracking system.

FIG. 13 is a schematic block diagram of one embodiment of an envelopetracking module.

FIG. 14 is a schematic block diagram of another embodiment of anenvelope tracking module.

FIG. 15 is a schematic block diagram of one embodiment of a phone board.

FIG. 16A is a schematic block diagram of one embodiment of an RF system.

FIG. 16B is a schematic block diagram of another embodiment of an RFsystem.

FIG. 17A is a schematic block diagram of a multi-band power amplifiersystem in accordance with one embodiment.

FIG. 17B is a schematic block diagram of a multi-band power amplifiersystem in accordance with another embodiment.

FIG. 18 shows one example of a graph of voltage versus time for theenvelope tracking system of FIG. 12.

FIG. 19 is a schematic block diagram of a multi-mode power amplifiermodule in accordance with one embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the claimed invention.

Overview of Example Power Amplifier Systems including Envelope Tracker

FIG. 1 is a schematic diagram of a power amplifier module (PAM) 10 foramplifying a radio frequency (RF) signal. The illustrated poweramplifier module 10 can be configured to amplify an RF signal (RF_IN) togenerate an amplified RF signal (RF_OUT). As described herein, the poweramplifier module 10 can include one or more power amplifiers.

FIG. 2 is a schematic block diagram of an example wireless or mobiledevice 11 that can include one or more of the power amplifier modules 10of FIG. 1. The wireless device 11 can also include an envelope trackingsystem implementing one or more features of the present disclosure.

The example wireless device 11 depicted in FIG. 2 can represent amulti-band and/or multi-mode device such as a multi-band/multi-modemobile phone. By way of examples, Global System for Mobile (GSM)communication standard is a mode of digital cellular communication thatis utilized in many parts of the world. GSM mode mobile phones canoperate at one or more of four frequency bands: 850 MHz (approximately824-849 MHz for Tx, 869-894 MHz for Rx), 900 MHz (approximately 880-915MHz for Tx, 925-960 MHz for Rx), 1800 MHz (approximately 1710-1785 MHzfor Tx, 1805-1880 MHz for Rx), and 1900 MHz (approximately 1850-1910 MHzfor Tx, 1930-1990 MHz for Rx). Variations and/or regional/nationalimplementations of the GSM bands are also utilized in different parts ofthe world.

Code division multiple access (CDMA) is another standard that can beimplemented in mobile phone devices. In certain implementations, CDMAdevices can operate in one or more of 800 MHz, 900 MHz, 1800 MHz and1900 MHz bands, while certain W-CDMA and Long Term Evolution (LTE)devices can operate over, for example, about 22 radio frequency spectrumbands.

One or more features of the present disclosure can be implemented in theforegoing example modes and/or bands, and in other communicationstandards. For example, 802.11, 2G, 3G, 4G, LTE, and Advanced LTE arenon-limiting examples of such standards.

In certain embodiments, the wireless device 11 can include switches 12,a transceiver 13, an antenna 14, power amplifiers 17, a controlcomponent 18, a computer readable medium 19, a processor 20, a battery21, and an envelope tracker 30.

The transceiver 13 can generate RF signals for transmission via theantenna 14. Furthermore, the transceiver 13 can receive incoming RFsignals from the antenna 14.

It will be understood that various functionalities associated with thetransmission and receiving of RF signals can be achieved by one or morecomponents that are collectively represented in FIG. 2 as thetransceiver 13. For example, a single component can be configured toprovide both transmitting and receiving functionalities. In anotherexample, transmitting and receiving functionalities can be provided byseparate components.

Similarly, it will be understood that various antenna functionalitiesassociated with the transmission and receiving of RF signals can beachieved by one or more components that are collectively represented inFIG. 2 as the antenna 14. For example, a single antenna can beconfigured to provide both transmitting and receiving functionalities.In another example, transmitting and receiving functionalities can beprovided by separate antennas. In yet another example, different bandsassociated with the wireless device 11 can be provided with differentantennas.

In FIG. 2, one or more output signals from the transceiver 13 aredepicted as being provided to the antenna 14 via one or moretransmission paths 15. In the example shown, different transmissionpaths 15 can represent output paths associated with different bandsand/or different power outputs. For instance, the two example poweramplifiers 17 shown can represent amplifications associated withdifferent power output configurations (e.g., low power output and highpower output), and/or amplifications associated with different bands.Although FIG. 2 illustrates a configuration using two transmission paths15 and two power amplifiers 17, the wireless device 11 can be adapted toinclude more or fewer transmission paths 15 and/or more or fewer poweramplifiers 17.

In FIG. 2, one or more detected signals from the antenna 14 are depictedas being provided to the transceiver 13 via one or more receiving paths16. In the example shown, different receiving paths 16 can representpaths associated with different bands. For example, the four examplepaths 16 shown can represent quad-band capability that some wirelessdevices are provided with. Although FIG. 2 illustrates a configurationusing four receiving paths 16, the wireless device 11 can be adapted toinclude more or fewer receiving paths 16.

To facilitate switching between receive and transmit paths, the switches12 can be configured to electrically connect the antenna 14 to aselected transmit or receive path. Thus, the switches 12 can provide anumber of switching functionalities associated with operation of thewireless device 11. In certain embodiments, the switches 12 can includea number of switches configured to provide functionalities associatedwith, for example, switching between different bands, switching betweendifferent power modes, switching between transmission and receivingmodes, or some combination thereof. The switches 12 can also beconfigured to provide additional functionality, including filteringand/or duplexing of signals.

FIG. 2 shows that in certain embodiments, a control component 18 can beprovided for controlling various control functionalities associated withoperations of the switches 12, the power amplifiers 17, the envelopetracker 30, and/or other operating components.

In certain embodiments, a processor 20 can be configured to facilitateimplementation of various processes described herein. The processor 20can implement various computer program instructions. The processor 20can be a general purpose computer, special purpose computer, or otherprogrammable data processing apparatus.

In certain embodiments, these computer program instructions may also bestored in a computer-readable memory 19 that can direct the processor 20to operate in a particular manner, such that the instructions stored inthe computer-readable memory 19.

The illustrated wireless device 11 also includes the envelope tracker30, which can be used to provide a power amplifier supply voltage to oneor more of the power amplifiers 17. For example, the envelope tracker 30can be configured to change the supply voltage provided to the poweramplifiers 17 based upon an envelope of the RF signal to be amplified.In the illustrated implementation, the envelope signal is provided tothe envelope tracker 30 from the transceiver 13. However, otherimplementations are possible, including, for example, configurations inwhich the envelope signal is provided to the envelope tracker 30 from abaseband processor or a power management integrated circuit (PMIC).Furthermore, in certain implementations, the envelope signal can begenerated from the RF signal by detecting the RF signal's envelope usingany suitable envelope detector.

The envelope tracker 30 can be electrically connected to the battery 21,which can be any suitable battery for use in the wireless device 11,including, for example, a lithium-ion battery. As will be described indetail further below, by controlling the voltage provided to one or moreof the power amplifiers 17, the power consumed from the battery 21 canbe reduced, thereby improving the battery life of the wireless device11.

FIG. 3A is a schematic block diagram of one example of a power amplifiersystem 26 including an envelope tracker 30. The illustrated poweramplifier system 26 includes the switches 12, the antenna 14, thebattery 21, a directional coupler 24, the envelope tracker 30, a poweramplifier 32, and a transceiver 33. The illustrated transceiver 33includes a baseband processor 34, an envelope shaping block 35, adigital-to-analog converter (DAC) 36, an I/Q modulator 37, a mixer 38,and an analog-to-digital converter (ADC) 39.

The baseband processor 34 can be used to generate an I signal and a Qsignal, which correspond to signal components of a sinusoidal wave orsignal of a desired amplitude, frequency, and phase. For example, the Isignal can be used to represent an in-phase component of the sinusoidalwave and the Q signal can be used to represent a quadrature component ofthe sinusoidal wave, which can be an equivalent representation of thesinusoidal wave. In certain implementations, the I and Q signals can beprovided to the I/Q modulator 37 in a digital format. The basebandprocessor 34 can be any suitable processor configured to process abaseband signal. For instance, the baseband processor 34 can include adigital signal processor, a microprocessor, a programmable core, or anycombination thereof. Moreover, in some implementations, two or morebaseband processors 34 can be included in the power amplifier system 26.

The I/Q modulator 37 can be configured to receive the I and Q signalsfrom the baseband processor 34 and to process the I and Q signals togenerate an RF signal. For example, the I/Q modulator 37 can includeDACs configured to convert the I and Q signals into an analog format,mixers for upconverting the I and Q signals to radio frequency, and asignal combiner for combining the upconverted I and Q signals into an RFsignal suitable for amplification by the power amplifier 32. In certainimplementations, the I/Q modulator 37 can include one or more filtersconfigured to filter frequency content of signals processed therein.

The envelope shaping block 35 can be used to convert envelope oramplitude data associated with the I and Q signals into shaped envelopedata. Shaping the envelope data from the baseband processor 34 can aidin enhancing performance of the power amplifier system 26 by, forexample, adjusting the envelope signal to optimize linearity of thepower amplifier 32 and/or to achieve a desired gain compression of thepower amplifier 32. In certain implementations, the envelope shapingblock 35 is a digital block, and the DAC 36 is used to convert theshaped envelope data into an analog envelope signal suitable for use bythe envelope tracker 30. However, in other implementations, the DAC 36can be omitted in favor of providing the envelope tracker 30 with adigital envelope signal to aid the envelope tracker 30 in furtherprocessing of the envelope signal.

The envelope tracker 30 can receive the envelope signal from thetransceiver 33 and a battery voltage V_(BATT) from the battery 21, andcan use the envelope signal to generate a power amplifier supply voltageV_(CC) _(_) _(PA) for the power amplifier 32 that changes in relation tothe envelope. The power amplifier 32 can receive the RF signal from theI/Q modulator 37 of the transceiver 33, and can provide an amplified RFsignal to the antenna 14 through the switches 12.

The directional coupler 24 can be positioned between the output of thepower amplifier 32 and an input of the switches 12, thereby allowing anoutput power measurement of the power amplifier 32 that does not includeinsertion loss of the switches 12. The sensed output signal from thedirectional coupler 24 can be provided to the mixer 38, which canmultiply the sensed output signal by a reference signal of a controlledfrequency so as to downshift the frequency spectrum of the sensed outputsignal. The downshifted signal can be provided to the ADC 39, which canconvert the downshifted signal to a digital format suitable forprocessing by the baseband processor 34. By including a feedback pathbetween the output of the power amplifier 32 and an input of thebaseband processor 34, the baseband processor 34 can be configured todynamically adjust the I and Q signals and/or envelope data associatedwith the I and Q signals to optimize the operation of the poweramplifier system 26. For example, configuring the power amplifier system26 in this manner can aid in controlling the power added efficiency(PAE) and/or linearity of the power amplifier 32.

Although the power amplifier system 26 is illustrated as include asingle power amplifier, the teachings herein are applicable to poweramplifier systems including multiple power amplifiers, including, forexample, multi-mode and/or multi-mode power amplifier systems.

FIG. 3B is a schematic block diagram of another example of a poweramplifier system 40 including an envelope tracker 30. The illustratedpower amplifier system 40 includes the envelope tracker 30, the poweramplifier 32, an inductor 27, an impedance matching block 31, theswitches 12, and the antenna 14. The illustrated envelope tracker 30 isconfigured to receive an envelope of the RF signal and to generate apower amplifier supply voltage V_(CC) _(_) _(PA) for the power amplifier32 using a battery voltage V_(BATT).

The illustrated power amplifier 32 includes a bipolar transistor 29having an emitter, a base, and a collector. The emitter of the bipolartransistor 29 can be electrically connected to a power low supplyvoltage V₁, which can be, for example, a ground supply. Additionally, aradio frequency (RF) signal can be provided to the base of the bipolartransistor 29. The bipolar transistor 29 can amplify the RF signal togenerate the amplified RF signal at the collector. The bipolartransistor 29 can be any suitable device. In one implementation, thebipolar transistor 29 is a heterojunction bipolar transistor (HBT).

The power amplifier 32 can be configured to provide the amplified RFsignal to the switches 12. The impedance matching block 31 can be usedto terminate the electrical connection between the power amplifier 32and the switches 12, which can aid in increasing power transfer and/orreducing reflections of the amplified RF signal generated using thepower amplifier 32.

The inductor 27 can be included to power the power amplifier 32 with thepower amplifier supply voltage V_(CC) _(_) _(PA) generated by theenvelope tracker 30 while choking or blocking high frequency RF signalcomponents. The inductor 27 can include a first end electricallyconnected to the envelope tracker 30, and a second end electricallyconnected to the collector of the bipolar transistor 29.

Although FIG. 3B illustrates one implementation of the power amplifier32, skilled artisans will appreciate that the teachings described hereincan be applied to a variety of power amplifier structures, such asmulti-stage power amplifiers and power amplifiers employing othertransistor structures. For example, in some implementations the bipolartransistor 29 can be omitted in favor of employing a field-effecttransistor (FET), such as a silicon FET, a gallium arsenide (GaAs) highelectron mobility transistor (HEMT), or a laterally diffused metal oxidesemiconductor (LDMOS) transistor. Additionally, the power amplifier 32can be adapted to include additional circuitry, such as biasingcircuitry.

FIGS. 4A-4B show two examples of power amplifier supply voltage versustime.

In FIG. 4A, a graph 47 illustrates one example of the voltage of an RFsignal 41 and a power amplifier supply voltage 43 versus time. The RFsignal 41 has an envelope 42.

It can be important that the power amplifier supply voltage 43 of apower amplifier has a voltage greater than that of the RF signal 41. Forexample, powering a power amplifier using a power amplifier supplyvoltage that has a magnitude less than that of the RF signal can clipthe RF signal, thereby creating signal distortion and/or other problems.Thus, it can be important the power amplifier supply voltage 43 begreater than that of the envelope 42. However, it can be desirable toreduce a difference in voltage between the power amplifier supplyvoltage 43 and the envelope 42 of the RF signal 41, as the area betweenthe power amplifier supply voltage 43 and the envelope 42 can representlost energy, which can reduce battery life and increase heat generatedin a wireless device.

In FIG. 4B, a graph 48 illustrates another example of the voltage of anRF signal 41 and a power amplifier supply voltage 44 versus time. Incontrast to the power amplifier supply voltage 43 of FIG. 4A, the poweramplifier supply voltage 44 of FIG. 4B changes in relation to theenvelope 42 of the RF signal 41. The area between the power amplifiersupply voltage 44 and the envelope 42 in FIG. 4B is less than the areabetween the power amplifier supply voltage 43 and the envelope 42 inFIG. 4A, and thus the graph 48 of FIG. 4B can be associated with a poweramplifier system having greater energy efficiency.

Overview of Envelope Tracking Systems

Apparatus and methods for envelope tracking are disclosed herein. Incertain implementations, an envelope tracking system for generating apower amplifier supply voltage for a power amplifier is provided. Theenvelope tracking system can include a buck converter and an erroramplifier configured to operate in parallel to control the voltage levelof the power amplifier supply voltage based on an envelope of an RFsignal amplified by the power amplifier. The buck converter can beconfigured to convert a battery voltage into a step down or buckvoltage, and the error amplifier can generate the power amplifier supplyvoltage by adjusting the magnitude of the step down voltage using a fastchanging output current

In certain implementations, the error amplifier can generate an errorcurrent than changes based on a magnitude of the error amplifier'soutput current, and the buck converter can control a magnitude of thebuck voltage based on the error current. Controlling the buck converterusing the error current can aid in improving the overall efficiency ofthe envelope tracking system. For example, the error amplifier can havea power efficiency that is less than a power efficiency of the buckconverter but a speed that is faster than a speed of the buck converter.Thus, configuring the buck converter to control the buck voltage andthus the power amplifier supply voltage based on the error current canhelp improve the overall power efficiency of the envelope trackingsystem by reducing the amount of current that the error amplifierprovides.

FIG. 5 is a schematic block diagram of one embodiment of an envelopetracking system 50. The envelope tracking system 50 includes the battery21, an error amplifier 51, a feedback circuit 52, a buck converter 53,and a boost converter 54.

The error amplifier 51 includes a first input configured to receive anenvelope signal (ENVELOPE), a second input electrically connected to afirst terminal of the feedback circuit 52, and an output electricallyconnected to the power amplifier supply voltage V_(CC) _(_) _(PA), to anoutput of the buck converter 53, and to a second terminal of thefeedback circuit 52. The error amplifier 51 is configured to generate anerror current I_(ERROR) and to provide the error current I_(ERROR) tothe buck converter 53.

The feedback circuit 52 can be any suitable circuit, and can includeactive and/or passive circuitry. In one implementation, the feedbackcircuit 52 includes a resistor electrically connected between thefeedback circuit's first and second terminals. However, any suitableimplementation of the feedback circuit 52 can be used.

The boost converter 54 is configured to receive a battery voltageV_(BATT) from the battery 21. The boost converter 54 is configured togenerate a boost voltage V_(BOOST), which can have a voltage levelgreater than a voltage level of the battery voltage V_(BATT). As shownin FIG. 5, the boost voltage V_(BOOST) can be used to power the erroramplifier 51. Although the boost converter 54 is illustrated asgenerating a single boosted output voltage, in certain implementationsthe boost converter 54 can be configured to generate a plurality ofboosted output voltages so as to provide other components or circuitrywith a power supply of a desired voltage level.

The buck converter 53 is configured to receive the battery voltageV_(BATT) from the battery 21 and the error current I_(ERROR) from theerror amplifier 51. The buck converter 53 includes an output configuredto control a voltage level of the power amplifier supply voltage V_(CC)_(_) _(PA) by sinking or sourcing current to the power amplifier supplyvoltage V_(CC) _(_) _(PA) through an internal inductor. The buckconverter 53 can be used to control the power amplifier supply voltageV_(CC) _(_) _(PA) to a voltage level that is less than a voltage levelof the battery voltage V_(BATT). As will be described in further detailbelow, the buck converter 53 can control the magnitude of the poweramplifier supply voltage V_(CC) _(_) _(PA) over time based on the errorcurrent I_(ERROR).

The illustrated envelope tracking system 50 includes the buck converter53 and the error amplifier 51, which have been configured to operate inparallel to control the voltage level of the power amplifier supplyvoltage V_(CC) _(_) _(PA) based on the envelope signal. The buckconverter 53 can have a power efficiency that is greater than the erroramplifier's power efficiency, but a tracking speed that is a slower thatthe error amplifier's tracking speed. Thus, the error amplifier 51 canbe used to provide tracking of high frequency components of the envelopesignal while the buck converter 53 can be used to provide tracking oflow frequency components of the envelope signal. In the illustratedconfiguration the error amplifier 51 is powered using the boost voltageV_(BOOST), and thus the error amplifier 51 can also be used to controlthe voltage level of the power amplifier supply voltage V_(CC) _(_)_(PA) to be above the battery voltage V_(BATT).

In the configuration shown in FIG. 5, the error amplifier 51 providesthe error current I_(ERROR) to the buck converter 53 to aid the buckconverter 53 in tracking the envelope signal. The error currentI_(ERROR) can indicate a difference between a current or present voltagelevel of the power amplifier supply voltage V_(CC) _(_) _(PA) and adesired voltage level of the power amplifier supply voltage V_(CC) _(_)_(PA). Since the error amplifier 51 can have a power efficiency that isless than a power efficiency of the buck converter 53 but a speed thatis faster than a speed of the buck converter 53, configuring the buckconverter 53 to control the power amplifier supply voltage V_(CC) _(_)_(PA) based on the error current I_(ERROR) can help improve the overallpower efficiency of the envelope tracking system 50 by reducing theamount of current that the error amplifier 51 provides. For example, theerror current I_(ERROR) can change as the error amplifier 51 sinks orsources current onto the power amplifier supply voltage V_(CC) _(_)_(PA), and the buck converter 53 can control the voltage level of thepower amplifier supply voltage V_(CC) _(_) _(PA) over time so as toreduce the magnitudes of the error current I_(ERROR) and the outputcurrent of the error amplifier 51.

As described earlier, the boost converter 54 can generate the boostvoltage V_(BOOST), which can have a voltage magnitude greater than thatof the battery voltage V_(BATT). Including the boost converter 54 in theenvelope tracking system 50 can allow the error amplifier 51 to controlthe power amplifier supply voltage V_(CC) _(_) _(PA) to a voltage levelabove the battery voltage V_(BATT). Configuring the envelope trackingsystem 50 in this manner can allow a power amplifier that is poweredusing the envelope tracking system 50 to drive a relatively large loadline impedance. For example, a power amplifier driving a large load lineimpedance can have relatively large voltage swings at the output of thepower amplifier when the power amplifier is amplifying a relative largeRF input signal. Thus, configuring the envelope tracking system 50 tocontrol the power amplifier supply voltage V_(CC) _(_) _(PA) above thebattery voltage V_(BATT) can increase the maximum load line impedancethat the power amplifier can drive by permitting the output signal ofthe power amplifier to exceed the battery voltage V_(BATT) withoutclipping or otherwise distorting the power amplifier's output signal.

The envelope tracking system 50 can provide numerous advantages overother envelope tracking schemes. For example, the envelope trackingsystem 50 can provide relatively robust envelope tracking whileproviding high power efficiency. Additionally, the envelope trackingsystem 50 can have a relatively small component count, including, forexample, a relatively small number of external components such asdiscrete inductors. In certain implementations, the envelope trackingsystem 50 is integrated on a common module such as a multi-chip module(MCM) with a power amplifier. However, other configurations arepossible.

FIG. 6 is a circuit diagram of one embodiment of a boost converter 60,which can be used, for example, in the envelope tracking system 50 ofFIG. 5. The boost converter 60 includes a boost circuit 63 and a boostcontrol block 64. The boost circuit 63 is configured to receive abattery voltage V_(BATT) and to boost or increase a voltage magnitude ofthe battery voltage V_(BATT) to generate a boost voltage V_(BOOST). Theboost control block 64 includes a feedback input configured to receivethe boost voltage V_(BOOST) and a control output for controlling theboost circuit 63.

The boost circuit 63 includes an inductor 65, first and second switches66 a, 66 b, and a bypass capacitor 67. The inductor 65 includes a firstend electrically connected to the battery voltage V_(BATT) and a secondend electrically connected to a first end of the first switch 66 a andto a first end of the second switch 66 b. The first switch 66 a furtherincludes a second end electrically connected to the first or power lowsupply voltage V₁, which can be, for example, a ground supply. Thesecond switch 66 b further includes a second end electrically connectedto the boost voltage V_(BOOST) and to a first end of the capacitor 67.The bypass capacitor 67 further includes a second end electricallyconnected to the power low supply voltage V₁. The bypass capacitor 67can be used to filter the boost voltage V_(BOOST). In certainimplementation the bypass capacitor 67 can be placed or positioned arelatively short distance from the boost converter's load.

The boost control block 64 can be configured to control the boostcircuit 63 so as to generate the boost voltage V_(BOOST). For instance,when the boost circuit 63 is operating continuously, the boost controlblock 64 can generate the boost voltage V_(BOOST) by regularly switchingthe state of the first and second switches 66 a, 66 b between aconfiguration associated with a first boost phase of the boost circuit63 and a configuration associated with a second boost phase of the boostcircuit 63. For example, during the first boost phase of the boostcircuit 63, the boost control block 64 can open the second switch 66 band close the first switch 66 a so as to increase the magnetic field ofthe inductor 65 by providing a current from the battery voltage V_(BATT)to the power low supply voltage V₁ through the inductor 65 and the firstswitch 66 a. Additionally, during the second boost phase of the boostcircuit 63, the boost control block 64 can close the second switch 66 band open the first switch 66 a such that the magnetic field of theinductor 65 generates a current from the battery voltage V_(BATT) to theboost voltage V_(BOOST) through the inductor 65 and the second switch 66b.

Although the boost circuit 63 has been described as being operated overtwo phases when generating the boost voltage V_(BOOST), the boostcircuit 63 can be configured to operate using additional phases. Forinstance, the boost circuit 63 can be configured to operateintermittently using the boost control block 64 by switching the boostcircuit 63 between the first boost phase, the second boost phase, and athird boost phase associated with opening the first and second switches66 a, 66 b.

Although FIG. 6 illustrate one example of a boost converter 60 suitablefor use in the envelope tracking systems described herein, otherconfigurations of the boost converter 60 can be used, including, forexample, configurations in which the first and second switches 66 a, 66b are connected and/or operated in other ways.

FIG. 7 is a circuit diagram of one embodiment of a buck converter 70,which can be used, for example, in the envelope tracking system 50 ofFIG. 5. The buck converter 70 includes a buck circuit 73 and a buckcontrol block 74. The buck circuit 73 is configured to receive a batteryvoltage V_(BATT) and to generate a buck voltage V_(BUCK), which can havea voltage magnitude less than that of the battery voltage V_(BATT). Thebuck control block 74 includes a feedback input configured to receivethe buck voltage V_(BUCK), an error input for receiving an error currentI_(ERROR), and a control output for controlling the buck circuit 73. Asdescribed above with reference to FIG. 5, the buck converter 70 can beelectrically connected in parallel with an error amplifier to generate apower amplifier supply voltage. Accordingly, in certain implementationsthe output of the buck converter 70 configured to generate the buckvoltage V_(BUCK) is electrically connected to the power amplifier supplyvoltage.

The buck circuit 73 includes an inductor 75, first and second switches76 a, 76 b, and a bypass capacitor 77. The first switch 76 a includes afirst end electrically connected to the battery voltage V_(BATT) and asecond end electrically connected to a first end of the second switch 76b and to a first end of the inductor 75. The second switch 76 b furtherincludes a second end electrically connected to the power low supplyvoltage V₁. The inductor 76 further includes a second end electricallyconnected to the buck voltage V_(BUCK) and to a first end of the bypasscapacitor 77. The bypass capacitor 77 further includes a second endelectrically connected to the power low supply voltage V₁. The bypasscapacitor 77 can be used to filter the buck voltage V_(BUCK). In certainimplementation the bypass capacitor 77 can be placed relatively close ornear to the buck converter's load.

The buck control block 74 can be configured to control the buck circuit73 so as to generate the buck voltage V_(BUCK). For instance, when thebuck circuit 73 is operating continuously, the buck control block 74 cangenerate the buck voltage V_(BUCK) by regularly switching the state ofthe first and second switches 76 a, 76 b between a configurationassociated with a first buck phase of the buck circuit 73 and aconfiguration associated with a second buck phase of the buck circuit73. For example, during the first buck phase of the buck circuit 73, thebuck control block 74 can open the second switch 76 b and close thefirst switch 76 a so as to charge the magnetic field of the inductor 75by providing a current from the battery voltage V_(BATT) to the buckvoltage V_(BUCK) through the inductor 75 and the first switch 76 a.Additionally, during the second buck phase of the buck circuit 73, thebuck control block 74 can be configured to close the second switch 76 band to open the first switch 76 a such that the magnetic field of theinductor 75 generates a current from the power low supply voltage V₁ tothe buck voltage V_(BUCK) through the second switch 76 b and theinductor 75.

Although the buck circuit 73 has been described as being operated overtwo phases when generating the buck voltage V_(BUCK), the buck circuit73 can be configured to operate using additional phases. For instance,the buck circuit 73 can be configured to operate intermittently with thebuck control block 74 configured to switch the buck circuit 73 betweenthe first buck phase, the second buck phase, and a third buck phaseassociated with opening each of the first and second switches 76 a, 76b.

The buck control block 74 includes a hysteretic current comparator 77,which can be used to control the buck circuit 73 based on the errorcurrent I_(ERROR). As was described earlier with respect to FIG. 5, theerror current I_(ERROR) can change in relation to an output current ofan error amplifier. The hysteretic current comparator 77 can be used tocontrol a magnitude of the buck voltage V_(BUCK) based on the errorcurrent I_(ERROR) so as to reduce an output current of the erroramplifier and to improve the overall efficiency of the envelope trackingsystem. In certain implementations, the error current I_(ERROR) is adifferential error current, and the hysteretic current comparator 77 isconfigured to compare a positive or non-inverted current component ofthe error current I_(ERROR) to a negative or inverted current componentof the error current I_(ERROR), and to control the buck voltage V_(BUCK)based on the result. Additional details of the hysteretic currentcomparator 77 can be as described further below.

Although FIG. 7 illustrate one example of a buck converter 70 suitablefor use in the envelope tracking systems described herein, other buckconverter configurations can be used.

FIG. 8 is a circuit diagram of one embodiment of a hysteretic currentcomparator 80, which can be used, for example, in the buck converter 70of FIG. 7. The hysteretic current comparator 80 includes first to ninthn-type field-effect transistors (NFETs) 81-89 and first to fourth p-typefield-effect transistors (PFETs) 91-94. The hysteretic currentcomparator 80 is configured to receive a reference current I_(REF) and adifferential error current I_(ERROR+), I_(ERROR−), and to generate anoutput signal OUT that can be used to control a buck converter. Thedifferential error current I_(ERROR+), I_(ERROR−) can correspond to adifference between a positive or non-inverted error current I_(ERROR+)and a negative or inverted error current I_(ERROR−).

The first NFET 81 includes a drain configured to receive the referencecurrent I_(REF). The drain of the first NFET 81 is electricallyconnected to a gate of the first NFET 81 and to a gate of the secondNFET 82. The second NFET 82 further includes a drain electricallyconnected to a drain of the first PFET 91. The first and second NFETs81, 82 each include a source electrically connected to the power lowsupply voltage V₁, which can be, for example, a ground supply. The thirdNFET 83 includes a drain configured to receive the negative errorcurrent I_(ERROR−). The drain of the third NFET 83 is electricallyconnected to a gate of the third NFET 83 and to a gate of the fourthNFET 84. The fourth NFET 84 further includes a drain electricallyconnected to a gate of the first PFET 91, to a gate and a drain of thesecond PFET 92, to a drain of the seventh NFET 87, to a drain of thethird PFET 93, to a gate of the ninth NFET 89, and to a gate of thefourth PFET 94. The third and fourth NFETs 83, 84 each further include asource electrically connected to the power low supply voltage V₁. Thefirst and second PFETs 91, 92 each further include a source electricallyconnected to a second or power high supply voltage V₂. In certainimplementations the power high supply voltage V₂ is a boost voltagegenerated by a boost converter. However, in other implementations thepower high supply voltage V₂ can be other voltages, such as a batteryvoltage.

The fifth NFET 85 includes a drain configured to receive the positiveerror current I_(ERROR+). The drain of the fifth NFET 85 is electricallyconnected to a gate of the fifth NFET 85 and to a gate of the sixth NFET86. The sixth NFET 86 further includes a drain electrically connected toa source of the seventh NFET 87 and to a source of the eighth NFET 88.The fifth and sixth NFETs 85, 86 each further include a sourceelectrically connected to the power low supply voltage V₁. The seventhNFET 87 further includes a gate electrically connected to a bias voltageV_(BIAS). In one implementation, the bias voltage V_(BIAS) is biasedwith a voltage level selected to be in the range of about 2.2 V to about3.6 V. However, persons of ordinary skill in the art will readilyascertain other suitable voltage values, including, for example, voltagevalues associated with a particular application and/or manufacturingprocess.

The eighth NFET 88 further includes a drain electrically connected tothe power high supply voltage V₂, and a gate electrically connected to agate of the third PFET 93, to a drain of the fourth PFET 94, and to adrain of the ninth NFET 89 at a node configured to generate the outputsignal OUT. The ninth NFET 89 further includes a source electricallyconnected to the power low supply voltage V₁, and the fourth PFET 94further includes a source electrically connected to the power highsupply voltage V₂.

The output signal OUT can change in relation to the differential errorcurrent I_(ERROR+), I_(ERROR−). For example, when the positive errorcurrent I_(ERROR+) is relatively large, the voltage of the gates of theninth NFET 89 and the fourth PFET 94 can be pulled high and the ninthNFET 89 and the fourth PFET 94 can control the output signal OUT to belogically low. Additionally, when the negative error current I_(ERROR−)is relatively large, the voltage of the gates of the ninth NFET 89 andthe fourth PFET 94 can be pulled low and the ninth NFET 89 and thefourth PFET 94 can control the output signal OUT to be logically high.Accordingly, the output signal OUT can track the differential errorcurrent I_(ERROR+), I_(ERROR−). Although the illustrated configurationillustrates one configurations of the output signal OUT, the teachingsherein are applicable to configurations in which the polarity of theoutput signal OUT is reversed.

The illustrated error amplifier 80 employs hysteresis to prevent theoutput signal OUT from changing state in response to relatively smallfluctuations of the differential error current I_(ERROR+), I_(ERROR−).For example, the eighth NFET 88 and the third PFET 93 can providehysteresis.

Although FIG. 8 illustrates one example of a hysteretic currentcomparator 80 for use in the buck converter 70 of FIG. 7, otherimplementations of the hysteretic current comparator 80 can be used,including arrangements having transistors arranged in other ways.Additionally, in some implementations the hysteretic current comparator80 can be omitted in favor of controlling the buck converter in otherways, such as by using a low pass filter.

FIG. 9 is a circuit diagram of one embodiment of an error amplifier 100,which can be used, for example, in the envelope tracking system 50 ofFIG. 5. The error amplifier 100 includes first to eighth NFETs 101-108,first to ninth PFETs 111-119, and a bias circuit 120. The erroramplifier 100 is configured to receive a differential input voltageV_(IN+), V_(IN−), to generate an output voltage V_(OUT), and to generatea differential error current I_(ERROR+), I_(ERROR−). The differentialinput voltage V_(IN+), V_(IN−) can be associated with a differencebetween a positive or first input voltage V_(IN+) and a negative orsecond input voltage V_(IN−).

The first PFET 111 includes a gate configured to receive the positiveinput voltage V_(IN+), and a source electrically connected to a sourceof the second PFET 112 and to a drain of the third PFET 113. The firstPFET 111 further includes a drain electrically connected to a drain ofthe first NFET 101, to a drain of the third NFET 103, and to a source ofthe fifth NFET 105. The second PFET 112 further includes a gateconfigured to receive the negative input voltage V_(IN−), and a drainelectrically connected to a drain of the second NFET 102, to a drain ofthe fourth NFET 104, and to a source of the sixth NFET 106. The thirdPFET 113 further includes a gate configured to receive a first biasvoltage V_(BIAS1), and a source electrically connected to the power highsupply voltage V₂. The first NFET 101 further includes a gateelectrically connected to a gate of the second NFET 102, to a gate ofthe third NFET 103, and to a gate of the fourth NFET 104 at a nodeconfigured to receive a second bias voltage V_(BIAS2). The first tofourth NFETs 101-104 each further include a source electricallyconnected to the power low supply voltage V₁.

The fifth NFET 105 further includes a gate electrically connected to agate of the sixth NFET 106 at a node configured to receive a third biasvoltage V_(BIAS3). The fifth NFET 105 further includes a drainelectrically connected to a gate of the sixth PFET 116, to a gate of theseventh PFET 117, and to a drain of the fourth PFET 114. The fourth PFET114 further includes a gate electrically connected to a gate of thefifth PFET 115 at a node configured to receive a fourth bias voltageV_(BIAS4). The fourth PFET 114 further includes a source electricallyconnected to a drain of the sixth PFET 116. The sixth and seventh PFETs116, 117 each further include a source electrically connected to thepower high supply voltage V₂. The seventh PFET 117 further includes adrain electrically connected to a source of the fifth PFET 115. Thefifth PFET 115 further includes a drain electrically connected to a gateof the eighth PFET 118, to a gate of the ninth PFET 119, and to a firstterminal of the bias circuit 120.

The eighth PFET 118 further includes a drain electrically connected to adrain of the seventh NFET 107 and configured to generate the outputvoltage V_(OUT). The ninth PFET 119 further includes a drain configuredto generate the positive error current I_(ERROR+). The eighth and ninthPFETs 118, 119 each further include a source electrically connected tothe power high supply voltage V₂. The eighth NFET 108 further includes adrain configured to generate the negative error current I_(ERROR−), anda gate electrically connected to a gate of the seventh NFET 107, to adrain of the sixth NFET 106, and to a second terminal of the biascircuit 120. The seventh and eighth NFETs 107, 108 each further includea source electrically connected to the power low supply voltage V₁.

The bias circuit 120 can be any suitable bias circuit. For example, inone implementation the bias circuit 120 includes a PFET and an NFETelectrically connected in parallel with the channels of the PFET and theNFET disposed between the first and second terminals of the bias circuit120. However, other configurations of the bias circuit 120 can be used.

The error amplifier 100 can be used to amplify the differential inputvoltage V_(IN+), V_(IN−) to generate the output voltage V_(OUT). Forexample, the first and second PFETs 111, 112 can operate as adifferential transistor pair, and the first to sixth NFETs 101-106 andthe fourth to seventh PFETs 114-117 can operate as a folded cascodeamplification structure. Additionally, the seventh NFET 107 and theeighth PFET 118 can operate as an output stage of the error amplifier100.

As shown in FIG. 9, the eighth NFET 108 and the ninth PFET 119 can beconfigured to receive the gate voltages of the seventh NFET 107 and theeighth PFET 118, respectively. Since the seventh NFET 107 and the eighthPFET 118 can operate as an output stage of the error amplifier 100,electrically connecting the gates of the eighth NFET 108 and the ninthPFET 119 in this manner can be used to generate a differential errorcurrent I_(ERROR+), I_(ERROR−) that tracks the output current of theerror amplifier 100. In certain implementations, the eighth NFET 108 isa replica transistor of the seventh NFET 107, and the ninth PFET 119 isa replica transistor of the eighth PFET 118. For example, in embodimentthe widths of the eighth NFET 108 and the ninth PFET 119 are selected tobe between about 100 times to about 200 times smaller than the widths ofthe seventh NFET 107 and the eighth PFET 118, respectively. However,persons having ordinary skill in the art will readily ascertain othersuitable widths.

The first to fourth bias voltages V_(BIAS1)-V_(BIAS4) can be anysuitable voltages. In one implementation, the first bias voltageV_(BIAS1) has a voltage level selected to be in the range of about 2 Vto about 3.8 V, the second bias voltage V_(BIAS2) has a voltage levelselected to be in the range of about 0.6 V to about 1 V, the third biasvoltage V_(BIAS3) has a voltage level selected to be in the range ofabout 2.2V to about 3.6 V, and the fourth bias voltage V_(BIAS4) has avoltage level selected to be in the range of about 2.4V to about 3.8 V.However, other voltage levels will be readily ascertained by personshaving ordinary skill in the art, including, for example, voltage levelsassociated with a particular application and/or process.

Although FIG. 9 illustrates one example of an error amplifier suitablefor use with the envelope tracking systems described herein, other erroramplifier configurations can be used in accordance with the envelopetracking schemes described herein.

FIG. 10 is a schematic block diagram of another embodiment of anenvelope tracking system 130. The envelope tracking system 130 includesthe battery 21, the error amplifier 51, the feedback circuit 52, and thebuck converter 53.

The envelope tracking system 130 of FIG. 10 is similar to the envelopetracking system 50 of FIG. 5, except that the envelope tracking system130 of FIG. 10 illustrates a configuration in which the boost converter54 of FIG. 5 has been omitted in favor of powering the error amplifier51 using the battery voltage V_(BATT). Configuring the envelope trackingsystem 130 in this manner can reduce the envelope tracking system'scomplexity by decreasing component count, such as a number of inductors.However, configuring the envelope tracking system 130 in this manner canalso reduce the maximum voltage level that the envelope tracking system130 can control the power amplifier supply voltage V_(CC) _(_) _(PA) to.For example, as described earlier with respect to FIG. 5, when a poweramplifier drives a relatively large load impedance, the power amplifiercan use a relatively large maximum power amplifier supply voltage.Accordingly, the envelope tracking system 130 can be suitable forpowering one or more power amplifiers that drive a relatively small loadline impedance, such as a load line impedance less than or equal to 5ΩAdditional details of the power amplifier system 130 can be similar tothose described earlier with respect to the power amplifier system 50 ofFIG. 5.

FIG. 11 shows one example of a graph 150 of current versus time for theenvelope tracking system 50 of FIG. 5. The graph 150 includes a firstplot 151 of current versus time, a second plot 152 of current versustime, and a third plot 153 of current versus time. The graph 150 cancorrespond to one example of current waveforms for certain envelopetracking systems described herein, such as the envelope tracking system50 of FIG. 5. For example, the first plot 151 can correspond to anoutput current of the error amplifier 51 versus time, the second plot152 can correspond to an output current of the buck converter 53 versustime, and the third plot 153 can correspond to a current provided to apower amplifier, which can be equal to the sum of the output current ofthe error amplifier 51 and the output current of the buck converter 53.As shown in the graph 150, by providing the error current signalI_(ERROR) to the buck converter 51, the buck converter 51 can beconfigured to generate a larger portion of the current provided to apower amplifier over time relative to the portion of current provided bythe error amplifier 51. Since the buck converter 53 can have a higherpower efficiency than the error amplifier 51, configuring the envelopetracking system in this way can improve power efficiency.

FIG. 12 is a schematic block diagram of another embodiment of anenvelope tracking system 160. The envelope tracking system 160 includesthe battery 21, the error amplifier 51, the feedback circuit 52, thebuck converter 53, an AC coupling capacitor 161, and a bypass capacitor162.

The envelope tracking system 160 of FIG. 12 is similar to the envelopetracking system 130 of FIG. 10, except that the envelope tracking system160 of FIG. 12 further includes the AC coupling capacitor 161 and thebypass capacitor 162. The bypass capacitor 162 is electrically connectedbetween the power amplifier supply voltage V_(CC) _(_) _(PA) and thepower low supply voltage V₁, and can be included to reduce output supplynoise. Additionally, the envelope tracking system 160 includes the ACcoupling capacitor 161, which has been electrically connected betweenthe output of the error amplifier 51 and the power amplifier supplyvoltage V_(CC) _(_) _(PA).

Inserting the AC coupling capacitor 161 in an electrical path betweenthe error amplifier's output and the power amplifier supply voltageV_(CC) _(_) _(PA) allows the error amplifier 51 to be powered using thebattery voltage V_(BATT) while permitting the error amplifier 51 tocontrol the power amplifier supply voltage V_(CC) _(_) _(PA) to voltagelevels above the battery voltage V_(BATT). Accordingly, the illustratedenvelope tracking system 160 can be used in applications associated witha relatively high maximum voltage level of the power amplifier supplyvoltage V_(CC) _(_) _(PA), such as configurations in which a poweramplifier drives a relatively large load impedance and has a relativelylarge output voltage swing.

In certain implementations, the envelope tracking system 160 isintegrated on a common module with a power amplifier. For example, inone embodiment, a multi-chip-module (MCM) includes a power amplifier dieand an envelope tracking die attached to a common module substrate.However, other implementations are possible, such as implementations inwhich the envelope tracking system 160 is implemented on an envelopetracking module that is separate from a power amplifier module.

FIG. 13 is a schematic block diagram of one embodiment of an envelopetracking module 170. The envelope tracking module 170 is configured togenerate a power amplifier supply voltage V_(CC) _(_) _(PA), which canbe used to power one or more power amplifiers.

The envelope tracking module 170 includes an envelope tracking die 171including first to seventh pins or pads 172 a-172 g, the buck controller74, the error amplifier 51, an n-type field effect transistor (NFET)174, and a p-type field effect transistor (PFET) 175. The envelopetracking module 170 further includes an inductor 55, the feedbackcircuit 52, the AC coupling capacitor 161, and the bypass capacitor 162.In certain implementations, the inductor 55, the feedback circuit 52,the AC coupling capacitor 161, and the bypass capacitor 162 areimplemented as components disposed on a module substrate of the poweramplifier module 170 on which the envelope tracking die 171 is attached.For example, the inductor 55, the feedback circuit 52, the AC couplingcapacitor 161, and/or the bypass capacitor 162 can be implemented atleast in part using surface mount components (SMCs). However, otherimplementations are possible. Although only certain components and pinshave been illustrated in FIG. 13 for clarity, the envelope trackingmodule 170 and/or the envelope tracking die 171 can be configured toinclude additional components and/or pins. Additionally, in certainimplementations, the inductor 55, the feedback circuit 52, the ACcoupling capacitor 161, and/or the bypass capacitor 162 can beimplemented in all or part on the envelope tracking die 171.

The buck controller 74 is electrically connected to the first orV_(BATT) pin 172 a, which can be used to provide power to the envelopetracking die 171. The buck controller 74 includes a first control outputelectrically connected to a gate of the NFET 174 and a second controloutput electrically connected to a gate of the PFET 175. The NFET 174further includes a source electrically connected to the power low supplyvoltage V₁ and a drain electrically connected to a drain of the PFET 175and to the second or BUCK_(OUT) pin 172 b. The PFET 175 further includesa source electrically connected to the V_(BATT) pin 172 a.

The buck controller 74 is configured to receive the error currentI_(ERROR) from the error amplifier 51. Additionally, the buck controller74 is electrically connected to the third or I_(HI) pin 172 c and to thefourth or I_(LO) pin 172 d, which can be used to provide thresholdcurrents that the buck controller 74 can compare to the error currentI_(ERROR). For example, the buck controller 74 can include thehysteretic current comparator 77, which can be configured to control theNFET 174 and the PFET 175 to increase the power amplifier supply voltageV_(CC) _(_) _(PA) when the error current I_(ERROR) is greater than thecurrent received on the I_(HI) pin 172 c and to decrease the poweramplifier supply voltage V_(CC) _(_) _(PA) when the error currentI_(ERROR) is less than the current received on the I_(LO) pin 172 d.Comparing the error current I_(ERROR) to threshold currents allows thebuck controller 74 to track a low frequency component of the poweramplifier supply voltage V_(CC) _(_) _(PA). Although one configurationof the buck controller 74 has been illustrated in FIG. 13, otherimplementations of the buck controller 74 can be used, such asconfigurations in which hysteresis is implemented in other ways.

The error amplifier 51 includes a non-inverted input electricallyconnected to the fifth or ENVELOPE pin 172 e, which can receive anenvelope signal associated with a power amplifier that is powered usingthe envelope tracking module 170. In certain implementations, theenvelope signal is provided by using at least one of a transceiver IC, abaseband processor, or a power management IC. The error amplifier 51further includes an inverted input electrically connected to the sixthor FBK pin 172 f. The error amplifier 51 further includes an outputelectrically connected to the seventh or ERR_(OUT) pin 172 g. The erroramplifier 51 is configured to generate the error current I_(ERROR) andto provide the error current T_(ERROR) to the buck controller 74.

The inductor 55 includes a first end electrically connected to theBUCK_(OUT) pin 172 b and a second end electrically connected to thepower amplifier supply voltage V_(CC) _(_) _(PA). The AC couplingcapacitor 161 includes a first end electrically connected to theERR_(OUT) pin 172 g and a second end electrically connected to the poweramplifier supply voltage V_(CC) _(_) _(PA). The bypass capacitor 162includes a first end electrically connected to the power amplifiersupply voltage V_(CC) _(_) _(PA) and a second end electrically connectedto the power low supply voltage V₁.

The illustrated envelope tracking module 170 can control the voltagelevel of the power amplifier supply voltage V_(CC) _(_) _(PA) using anenvelope signal received on the ENVELOPE pin 172 e. Additionally, theenvelope tracking module 170 employs a buck converter and an erroramplifier that operate in parallel to control the voltage level of thepower amplifier supply voltage V_(CC) _(_) _(PA). In particular, thebuck controller 74 including the hysteretic current comparator 77 can beused to track a low frequency component of the envelope signal, whilethe error amplifier 51 can be used to track a high frequency componentof envelope signal by controlling the AC current delivered to the poweramplifier supply voltage V_(CC) _(_) _(PA) based on a difference betweenthe envelope signal and a high frequency feedback signal received fromthe feedback circuit 52. Furthermore, since the output of the erroramplifier 51 is electrically connected to the power amplifier supplyvoltage V_(CC) _(_) _(PA) through the AC coupling capacitor 161, theenvelope tracking module 170 can be used to control the voltage level ofthe power amplifier supply voltage V_(CC) _(_) _(PA) to be above that ofa battery voltage received on the V_(BATT) pin 172 a.

As described in various configurations above, a buck converter can beconfigured to generate a buck voltage that has a magnitude based on anerror current generated by an error amplifier. However, buck converterscan be controlled in other ways. For example, in certainimplementations, a power amplifier voltage can be filtered and used togenerate a control voltage for controlling the buck converter. Forexample, in certain instances the filtered power amplifier supplyvoltage can be compared to a reference voltage to generate the controlvoltage.

FIG. 14 is a schematic block diagram of another embodiment of anenvelope tracking module 180. The envelope tracking module 180 isconfigured to generate a power amplifier supply voltage V_(CC) _(_)_(PA), which can be used to power one or more power amplifiers.

The envelope tracking module 180 includes an envelope tracking die 181including first to seventh pins or pads 182 a-182 g, an error amplifier183, an NFET 184, a PFET 185, a DC-to-DC controller 186, a referencevoltage generator 187, a low pass filter 188, and a comparator 228. Theenvelope tracking module 180 further includes an inductor 55, the ACcoupling capacitor 161, the bypass capacitor 162, a first feedbackresistor 189 a, and a second feedback resistor 189 b.

In certain implementations, the inductor 55, the AC coupling capacitor161, the bypass capacitor 162, and the first and second feedbackresistors 189 a, 189 b are implemented as components disposed on apackage substrate associated with the envelope tracking die 181.However, other implementations are possible. Although only certaincomponents and pins have been illustrated in FIG. 14 for clarity, theenvelope tracking module 180 and/or the envelope tracking die 181 can beconfigured to include additional components and/or pins.

The DC-to-DC controller 186 is electrically connected to the first orV_(BATT) pin 182 a. The DC-to-DC controller 186 includes a first controloutput electrically connected to a gate of the NFET 184 and a secondcontrol output electrically connected to a gate of the PFET 185. TheNFET 184 further includes a source electrically connected to the powerlow supply voltage V₁ and a drain electrically connected to a drain ofthe PFET 185 and to the second or V_(REG) pin 182 b. The PFET 185further includes a source electrically connected to the V_(BATT) pin 182a. The DC-to-DC controller 186 is configured to receive a controlvoltage V_(CONTROL) from the comparator 228. The DC-to-DC controller 186can be configured to control the gate voltages of the NFET 184 and thePFET 185 to control the voltage level of the power amplifier supplyvoltage V_(CC) _(_) _(PA) based on a voltage level of the controlvoltage V_(CONTROL), which can operate as a low frequency feedbacksignal. Although the DC-to-DC controller 186 is illustrated in a buckconverter configuration, the teachings herein are applicable to boostconverter configurations.

The error amplifier 183 includes a non-inverted input electricallyconnected to the third or ENVELOPE pin 182 c, which can be configured toreceive an envelope signal associated with the input signal of a poweramplifier that is powered using the envelope tracking module 180. Incertain implementations, the envelope signal is provided by using atleast one of a transceiver IC, a baseband processor, or a powermanagement IC. The error amplifier 183 further includes an invertedinput electrically connected to the fourth or FBK_(HIGH) pin 182 d,which has been configured to receive a high frequency feedback signalfrom the first and second feedback resistors 189 a, 189 b, as will bedescribed below. The error amplifier 183 further includes an outputelectrically connected to the fifth or ERR_(OUT) pin 182 e. AlthoughFIG. 14 illustrates a configuration in which resistors are used togenerate a high frequency feedback signal for an error amplifier, otherconfigurations are possible, including, for example, configurations thatomit resistors and/or include resistors arranged in other ways.

The low pass filter 188 includes an input electrically connected to thesixth of FBK_(LOW) pin 182 e, which has been configured to receive thepower amplifier supply voltage V_(CC) _(_) _(PA). The low pass filter188 can be configured to filter or attenuate high frequency componentsof the power amplifier supply voltage V_(CC) _(_) _(PA) to generate afiltered power amplifier supply voltage. The reference voltage generator187 can generate a reference voltage V_(REF), which the comparator 228can compare to the filtered power amplifier supply voltage to generatethe control voltage V_(CONTROL) used to control the DC-to-DC controller186.

In the illustrated configuration, the reference voltage generator 187 iselectrically connected to the seventh or SPI pin 182 g, which can beassociated with a data input pin of a serial peripheral interface (SPI).Although not illustrated in FIG. 14 for clarity, the envelope trackingmodule 180 can include additional pins associated with the serialperipheral interface, including, for example, a serial clock pin, a dataoutput pin, and/or a select pin. The SPI pin 182 g can be associatedwith a serial peripheral interface or bus used to provide data forcontrolling a voltage level of the reference voltage V_(REF). Forexample, the reference voltage generator 187 can include adigital-to-analog (D-to-A) converter that can convert digital datareceived on the SPI pin 182 g to an analog signal used to generate thereference voltage V_(REF). In certain implementations, the SPI pin 182 gcan be used to dynamically change the reference voltage V_(REF) tooptimize the energy efficiency of a power amplifier that the envelopetracking module 180 powers. For example, the reference voltage generator187 can be used to dynamically change the reference voltage V_(REF)between transmission slots of the power amplifier so as to, for example,change the characteristics of the power amplifier supply voltage V_(CC)_(_) _(PA) across different power modes.

The inductor 55 includes a first end electrically connected to theV_(REG) pin 182 b and a second end electrically connected to the poweramplifier supply voltage V_(CC) _(_) _(PA). The AC coupling capacitor161 includes a first end electrically connected to the ERR_(OUT) pin 182e and a second end electrically connected to the power amplifier supplyvoltage V_(CC) _(_) _(PA). The bypass capacitor 162 includes a first endelectrically connected to the power amplifier supply voltage V_(CC) _(_)_(PA) and a second end electrically connected to the power low supplyvoltage V₁. The first feedback resistor 189 a includes a first endelectrically connected to the FBK_(HIGH) pin 182 d and a second endelectrically connected to the ERR_(OUT) pin 182 e. The second feedbackresistor 189 b includes a first end electrically connected to the powerlow supply voltage V₁ and a second end electrically connected to theFBK_(HIGH) pin 182 d.

In the illustrated configuration, the error amplifier 183 receives ahigh frequency feedback signal from the first and second feedbackresistors 189 a, 189 b. For example, in the illustrated configuration,the AC coupling capacitor 161 has been disposed between the poweramplifier supply voltage V_(CC) _(_) _(PA) and the first and secondfeedback resistors 189 a, 189 b, thereby operating to block lowfrequency components of the power amplifier supply voltage V_(CC) _(_)_(PA) from reaching the inverted input of the error amplifier 183.Configuring the power amplifier module 180 in this manner can aid inincreasing the power efficiency of the module by allowing the DC-to-DCcontroller 186 to track low frequency changes in the envelope signal andthe error amplifier 183 to track high frequency changes in the envelopesignal.

In the illustrated configuration the error amplifier 183 operates usinghigh frequency feedback alone, and thus an error current generated bythe error amplifier 183 may not include low frequency informationsuitable for tracking by the DC-to-DC controller 186. Thus, rather thanusing an error current I_(ERROR) from the error amplifier 183 to controlthe DC-to-DC controller 186, the illustrated envelope tracking module180 filters the power amplifier supply voltage V_(CC) _(_) _(PA) usingthe low pass filter 188 and compares the filtered power amplifier supplyvoltage to the reference voltage V_(REF) to generate the control voltageV_(CONTROL), which operates as a low frequency feedback signal.

FIG. 15 is a schematic block diagram of one embodiment of a phone board190. The phone board 190 includes a transceiver IC 191, a powermanagement IC (PMIC) 192, and a power amplifier (PA) module 193. Thetransceiver IC 191 is configured to generate a radio frequency signal(RF SIGNAL) and an envelope signal (ENVELOPE). The PA module 193 isconfigured to receive the envelope signal and the radio frequency signalfrom the transceiver IC 191. Additionally, the PA module 193 isconfigured to receive a regulated voltage V_(REG) from the PMIC 192 andto provide a control voltage V_(CONTROL) to the PMIC 192. The PMIC 192can be configured to control a voltage level of the regulated voltageV_(REG) based on a voltage level of the control voltage V_(CONTROL).

The PA module 193 can be, for example, a multi-chip module (MCM)including one or more dies mounted on a surface of a module or carriersubstrate. By integrating a plurality of dies and/or other components ona module, a wide variety of advantages can be achieved, including, forexample, reduction of cost, improved ease of manufacture, and/orreduction in the length of interconnections.

The PMIC 192 can include one or more dies and/or other componentsconfigured to generate a regulated voltage for the PA module 193. ThePMIC 192 can include, for example, one or more DC-to-DC converters, lowdrop out (LDO) regulators, and/or other circuitry configured to generateone or more regulated supply voltages for components of the phone board190, including, for example, the PA module 193. The PMIC 192 can beconfigured to generate the one or more power supply voltages using abattery voltage from a battery. In certain implementations, the PMIC 192can include a battery charger for providing power path management to thebattery.

The PA module 193 can generate the control voltage V_(CONTROL), whichcan be used by the PMIC 192 to control a voltage level of the regulatedvoltage V_(REG) that is provided to the PA module 193. As will bedescribed in detail below, the PA module 193 can include an erroramplifier configured to adjust a voltage level of the regulated voltageV_(REG) based on the envelope signal ENVELOPE received from thetransceiver IC 191. Additionally, the PA module 193 can include feedbackcircuitry configured to adjust a voltage level of the control voltageV_(CONTROL). The PA module 193 can use the control voltage V_(CONTROL)to control a voltage level of the regulated voltage V_(REG) in a mannersimilar to that described earlier with respect to FIG. 14. Accordingly,the PA module 193 and the PMIC 192 can collectively operate to provideenvelope tracking to power amplifiers disposed on the PA module 193.

The phone board 190 of FIG. 9 includes an envelope tracking system forproviding envelope signal tracking without requiring a dedicatedenvelope tracking module or die. Thus, the phone board 190 can operateusing envelope tracking functionality while having reduced board costand/or area relative to a scheme in which a phone board includes adedicated envelope tracking module or die. Although FIG. 15 illustratesa configuration in which the envelope signal is generated using thetransceiver IC 191, other configurations are possible.

FIG. 16A is a schematic block diagram of one embodiment of an RF system200. The RF system 200 includes a power amplifier (PA) module 211 and apower management integrated circuit (PMIC) 201. In one embodiment, theRF system 200 is a portion of a phone board of a wireless device.

The PMIC 201 includes the NFET 184, the PFET 185, the DC-to-DCcontroller 186, first to third pins 202 a-202 c, a PMIC inductor 205,and a PMIC capacitor 207. Although the PMIC 201 is illustrated asincluding certain components and pins for clarity, the PMIC 201 can beadapted to include additional components and/or pins.

The DC-to-DC controller 186 includes a supply input electricallyconnected to the first or V_(BATT) pin 202 a, which can be configured toreceive a battery voltage V_(BATT) from a battery. The DC-to-DCcontroller 186 further includes a control input electrically connectedto the second or V_(CONTROL) pin 202 b. The DC-to-DC controller 186includes a first control output electrically connected to a gate of theNFET 184 and a second control output electrically connected to a gate ofthe PFET 185. The PFET 185 further includes a source electricallyconnected to the V_(BATT) pin 202 a and a drain electrically connectedto a drain of the NFET 184 and to a first end of the PMIC inductor 205.The NFET 184 further includes a source electrically connected to thepower low supply voltage V₁, and the PMIC inductor 205 further includesa second end electrically connected to the third or V_(REG) pin 202 c,which can be used to provide a regulated voltage to the power amplifiermodule 211. The PMIC capacitor 207 is electrically connected between theV_(REG) pin 202 c and the power low supply voltage V₁. The DC-to-DCcontroller 186 can be configured to control the gate voltages of theNFET 184 and the PFET 185 so as to control the voltage level of theV_(REG) pin 202 c based on a voltage level of a control voltage receivedon the V_(CONTROL) pin 202 b. Although the PMIC 201 is illustrated for abuck converter configuration, the PMIC 201 can be adapted to provide aboost voltage. Thus, the regulated voltage V_(REG) can be a buckvoltage, a boost voltage, or a voltage that changes between a buckvoltage and a boost voltage over time.

The power amplifier module 211 includes the power amplifier 32, the ACcoupling capacitor 161, the bypass capacitor 162, the error amplifier183, the reference voltage generator 187, the low pass filter 188, thefirst feedback resistor 189 a, the second feedback resistor 189 b, thefirst to seventh pins 212 a-212 g, an inductor 215, and the comparator228. Although the power amplifier module 211 is illustrated as includingcertain components and pins for clarity, the power amplifier module 211can be adapted to include additional components and/or pins.

The second feedback resistor 189 b includes a first end electricallyconnected to the power low supply voltage V₁ and a second endelectrically connected to an inverted input of the error amplifier 183and to a first end of the first feedback resistor 189 a. The firstfeedback resistor 189 a further includes a second end electricallyconnected to a first end of the AC coupling capacitor 161 and to anoutput of the error amplifier 183. The error amplifier 183 furtherincludes a supply input electrically connected to the first or V_(BATT)pin 212 a, which can be configured to receive the battery voltageV_(BATT). The error amplifier 183 further includes a non-inverted inputelectrically connected to the second or ENVELOPE pin 212 b. The ACcoupling capacitor 161 further includes a second end electricallyconnected to the power amplifier supply voltage V_(CC) _(_) _(PA).

The inductor 215 includes a first end electrically connected to thethird or V_(REG) pin 212 c and a second end electrically connected tothe power amplifier supply voltage V_(CC) _(_) _(PA). The capacitor 162includes a first end electrically connected to the power amplifiersupply voltage V_(CC) _(_) _(PA) and a second end electrically connectedto the power low supply voltage V₁. The low pass filter 188 includes aninput electrically connected to the power amplifier supply voltageV_(CC) _(_) _(PA) and an output electrically connected to a first inputof the comparator 228. The comparator 228 further includes an outputelectrically connected to the fourth or V_(CONTROL) pin 212 d and asecond input configured to receive a reference voltage V_(REF) from anoutput of the reference voltage generator 187. The reference voltagegenerator 187 further includes an input electrically connected to thefifth or SPI pin 212 e, which can be associated with a data input pin ofa serial peripheral interface. The power amplifier 32 includes a supplyinput configured to receive the power amplifier supply voltage V_(CC)_(_) _(PA), a signal input electrically connected to the sixth or RF_INpin 212 f, and a signal output electrically connected to the seventh orRF_OUT pin 212 g.

The low pass filter 188 can be configured to filter or attenuate highfrequency components of the power amplifier supply voltage V_(CC) _(_)_(PA) to generate a filtered power amplifier supply voltage for thecomparator 228. The comparator 228 can also receive the referencevoltage V_(REF) from the reference voltage generator 187, and cancompare the reference voltage V_(REF) to the filtered power amplifiersupply voltage to generate the control voltage V_(CONTROL) that is usedto control the DC-to-DC controller 186 of the PMIC 201. In theillustrated configuration, the reference voltage generator 187 iselectrically connected to the SPI pin 212 e, which can be coupled to aserial peripheral interface or bus that provides data for controlling avoltage level of the reference voltage V_(REF). For example, thereference voltage generator 187 can include a digital-to-analog (D-to-A)converter that can convert digital data received on the SPI pin 212 e toan analog signal used to generate the reference voltage V_(REF).

In the illustrated configuration, the AC coupling capacitor 161 has beendisposed between the power amplifier supply voltage V_(CC) _(_) _(PA)and the series combination of the first and second feedback resistors189 a, 189 b, thereby operating to block low frequency contentassociated with the power amplifier supply voltage V_(CC) _(_) _(PA)from reaching the inverted input of the error amplifier 183. Thus, theerror amplifier 183 shown in FIG. 16A operates using high frequencyfeedback alone. Additionally, the comparator 228 generates the controlvoltage V_(CONTROL), which operates as a low frequency feedback signalthat is based on a comparison of the filtered power amplifier supplyvoltage generated by the low pass filter 188 and the reference voltageV_(REF) generated by the reference voltage generator 187.

The RF system 200 illustrates a scheme in which the error amplifier 183has been included on the power amplifier module 211. Including both theerror amplifier 183 and the power amplifier 32 on the power amplifiermodule 211 can reduce the size of an inductor (such as the inductor 27of FIG. 3B) used to provide a supply voltage to the power amplifier 32.For example, the error amplifier 183 and the power amplifier 32 are bothelectrically connected to the second end of the inductor 215, and thus ahigh frequency error current generated by the error amplifier 183 neednot pass through the inductor 215 and contribute to the inductor'sL-dI/dt noise. Thus, integrating the error amplifier 183 on a commonmodule with the power amplifier 32 can reduce the size of the inductorused to provide a supply voltage to the power amplifier 32 for a givenamount of power supply noise.

FIG. 16B is a schematic block diagram of another embodiment of an RFsystem 220. The RF system 220 includes a power amplifier module 221 andthe PMIC 201. The RF system 220 of FIG. 16B of is similar to the RFsystem 200 of FIG. 16A, except that the RF system 220 of FIG. 16Bincludes a different power amplifier module configuration. Inparticular, in contrast to the power amplifier module 211 of FIG. 16A,the power amplifier module 221 of FIG. 16B further includes a high passfilter 216 and a comparator 229. The high pass filter 216 includes aninput configured to receive the power amplifier supply voltage V_(CC)_(_) _(PA) and an output configured to provide a filtered poweramplifier supply voltage to the comparator 229. The high pass filter 216can filter or remove low frequency components of the power amplifiersupply voltage V_(CC) _(_) _(PA) to generate a high pass filtered poweramplifier supply voltage. The comparator 229 is further configured toreceive an envelope signal from the ENVELOPE pin 212 b, and to comparethe high pass filtered power amplifier supply voltage to the envelopesignal to generate a high frequency envelope signal for the non-invertedinput of the error amplifier 183.

Although FIGS. 16A-16B illustrate configurations of RF systems thatinclude the AC coupling capacitor 161, in certain implementations, theAC coupling capacitor 161 can be omitted to reduce component count. Forexample, although omitting the AC coupling capacitor 161 can reduce themaximum voltage level that the error amplifier 183 can control the poweramplifier supply voltage V_(CC) _(_) _(PA) to, such RF systems can beused, for example, to power one or more power amplifiers that drive arelatively small load line impedance and thus have a relatively smalloutput voltage swing.

FIG. 17A is a schematic block diagram of a multi-band power amplifiersystem 230 in accordance with one embodiment. The illustrated multi-bandpower amplifier system 230 includes a first power amplifier module 231,a second power amplifier module 232, a third power amplifier module 233,and a power management IC 234. The first power amplifier module 231includes a first inductor 241, the second power amplifier module 232includes a second inductor 242, and the third power amplifier module 233includes a third inductor 243. Although the multi-band power amplifiersystem 230 is illustrated as including three power amplifier modules,the multi-band power amplifier system 230 can be adapted to include moreor fewer power amplifier modules.

The first to third power amplifier modules 231-233 can each beconfigured to communicate over a different RF communication band.Providing a plurality of power amplifiers in a multi-band poweramplifier system can aid in increasing power efficiency of the systemand/or in relaxing the design constraints of the power amplifiers, aseach power amplifier can be separately optimized for the particular bandthat the power amplifier amplifies.

The PMIC 234 has been configured to generate a regulated voltageV_(REG), which has been provided to a first end of each of the first tothird inductors 241-243. The first to third inductors 241-243 eachinclude a second end electrically connected to a power amplifier supplyvoltage local to each power amplifier module. For example, the firstinductor 241 includes a second electrically connected to a first poweramplifier supply voltage V_(CC) _(—PA1) associated with the first poweramplifier module 231, the second inductor 242 includes a second endelectrically connected to a second power amplifier supply voltage V_(CC)_(_) _(PA2) associated with the second power amplifier module 232, andthe third inductor 243 includes a second end electrically connected to athird power amplifier supply voltage V_(CC) _(_) _(PA3) associated withthe third power amplifier module 233. The first to third power amplifiermodules 231-233 have also been configured to generate first to thirdcontrol voltages V_(CONTROL1)-V_(CONTROL3), which have been provided tothe PMIC 234.

The PMIC 234 can be used to control the voltage level of the regulatedvoltage V_(REG) based on a control voltage received from an enabled oractive power amplifier module. For example, when a power amplifier onthe first power amplifier module 231 is enabled, the PMIC 234 can beused to control a voltage level of the first power amplifier supplyvoltage V_(CC) _(_) _(PA1) based on a voltage level of the first controlvoltage V_(CONTROL1). Similarly, when a power amplifier on the secondpower amplifier module 232 is enabled, the PMIC 234 can be used tocontrol a voltage level of the second power amplifier supply voltageV_(CC) _(_) _(PA2) based on a voltage level of the second controlvoltage V_(CONTROL2). Likewise, when a power amplifier on the thirdpower amplifier module 233 is enabled, the PMIC 234 can be used tocontrol a voltage level of the third power amplifier supply voltageV_(CC) _(_) _(PA3) based on a voltage level of the third control voltageV_(CONTROL3). In certain implementations, the first to third controlvoltages V_(CONTROL1)-V_(CONTROL3) can be provided to the PMIC 234 usinga shared electrical connection, such as a shared phone board trace, andthe multi-band power amplifier system 230 can be configured such that atmost one of the first to third control voltagesV_(CONTROL1)-V_(CONTROL3) is active at a time.

In a manner similar to that described earlier with respect to FIGS.14A-14B, each of the power amplifier modules 231-233 can include anerror amplifier used to adjust a respective power amplifier supplyvoltage to track the envelope of an RF signal amplified by the poweramplifier module. Thus, the multi-band power amplifier system 230 ofFIG. 17A illustrates an implementation in which the first to third poweramplifier supply voltages V_(CC) _(_) _(PA1)-V_(CC) _(_) _(PA3) can beenvelope tracking supplies which use a common regulated voltage V_(REG)generated by the PMIC 234.

FIG. 17B is a schematic block diagram of a multi-band power amplifiersystem 240 in accordance with another embodiment. The illustratedmulti-band power amplifier system 240 includes the first to third poweramplifier modules 231-233, the PMIC 234, and the first to thirdinductors 241-243. The multi-band power amplifier system 240 of FIG. 17Bis similar to the multi-band power amplifier system 230 of FIG. 17A,except that the multi-band power amplifier system 240 of FIG. 17Billustrates a configuration in which the first to third inductors241-243 have been disposed external to the first to third poweramplifier modules 231-233, respectively. For example, the first to thirdinductors 241-243 can be disposed on a phone board associated with themulti-band power amplifier system 240. The teachings herein areapplicable to configurations in which an inductor is implemented on apower amplifier module, implemented on a phone board, or a combinationthereof.

FIG. 18 shows one example of a graph 250 of voltage versus time for theenvelope tracking system 160 of FIG. 12. The graph 250 includes a firstplot 251 of voltage versus time and a second plot 252 of voltage versustime. The graph 250 can correspond to one example of the voltages of theenvelope tracking system 160 of FIG. 12. For example, the first plot 251can correspond to the power amplifier supply voltage V_(CC) _(_) _(PA)of FIG. 12 and the second plot 252 can correspond to the output voltageof the error amplifier 51 of FIG. 12.

FIG. 19 is a schematic block diagram of a multi-mode power amplifier(PA) module 260 in accordance with one embodiment.

The multi-mode PA module 260 includes a first or V_(BATT) pin 262 aconfigured to receive a battery voltage and a second or GND pin 262 bconfigured to receive a ground voltage. Additionally, the multi-mode PAmodule 260 further includes a third or HB_3G/4G pin 262 c configured toreceive a high band 3G/4G signal, which can be amplified by high band3G/4G power amplifier circuitry 263 and provided to a ninth pin 262 i.The amplified high band 3G/4G signal provided to the ninth pin 262 i canbe filtered using an external filter and/or duplexer. The multi-mode PAmodule 260 further includes a fourth or HB-2G pin 262 d that can receivea high band 2G signal, which can be amplified by high band 2G poweramplifier circuitry 264. The multi-mode PA module 260 further includes afifth or LB-2G pin 262 e configured to receive a low band 2G signal,which can be amplified by low band 2G power amplifier circuitry 265.Additionally, the multi-mode PA module 260 includes a sixth or LB_3G/4Gpin 262 f configured to receive a low band 3G/4G signal, which can beamplified by low band 3G/4G power amplifier circuitry 266 and providedto a thirteenth pin 262 m. The amplified low band 3G/4G signal providedto the thirteenth pin 262 m can be filtered using an external filterand/or duplexer.

A seventh pin 262 g (POWER CTRL) can be used to provide a power controlsignal to a power amplifier control block 270, which in certainimplementations can be a millimeter-wave mobile broadband (MMB) poweramplifier control system. The multi-mode PA module 260 further includesan eighth or serial peripheral interface (SPI) pin 262 h, which can beelectrically connected to a digital control block 269. The poweramplifier control block 270 and the digital control block 269 can beused to allow external circuitry to control the functionality of themulti-mode PA module 260, such as to select a power mode or active path.The power amplifier control block 270 and/or the digital control block269 can be configured to control other components or blocks of themulti-mode PA module 260. For example, in the illustrated configuration,the power amplifier control block 270 is configured to control a switchcontrol block 268.

The switch control block 268 can be used to select the active path ofthe multi-mode PA module 260 by controlling the switch 267. In theillustrated configuration, the switch 267 is a double-pole seven-throw(DP7T) switch configured to receive seven input signals. In particular,the switch 267 is configured to receive a first signal from a twelfth orPCS pin 262 l, a second signal from an eleventh or DCS pin 262 k, athird signal from a tenth or RX1 pin 262 j, a fourth signal from thehigh band 2G power amplifier circuitry 264, a fifth signal from the lowband 2G power amplifier circuitry 265, a sixth signal from a fourteenthor RX2 pin 262 n, and a seventh signal from a fifteenth or GSM pin 262o. The switch 267 includes a first output electrically connected to asixteenth pin 262 p, which can be connected to a high band antenna (HBANT). The switch 267 further includes a second output electricallyconnected to a seventeenth pin 262 q, which can be connected to a lowband antenna (LB ANT). A directional coupler 275 can be used to sensesignals provided to the high band and low band antennas on the sixteenthand seventeenth pins 262 p, 262 q, respectively. The directional coupler275 includes a first port electrically connected to an eighteenth pin262 r and a second port electrically connected to a nineteenth pin 262s.

Although FIG. 19 illustrates one example of a multi-mode PA, themulti-mode PA can be implemented in other implementations, includingconfigurations using a different arrangement of circuitry,configurations that amplify a different combination of signal bands, andconfigurations using more or fewer components and/or pins.

Applications

Some of the embodiments described above have provided examples inconnection with wireless devices or mobile phones. However, theprinciples and advantages of the embodiments can be used for any othersystems or apparatus that have needs for envelope trackers.

Such envelope trackers can be implemented in various electronic devices.Examples of the electronic devices can include, but are not limited to,consumer electronic products, parts of the consumer electronic products,electronic test equipment, etc. Examples of the electronic devices canalso include, but are not limited to, memory chips, memory modules,circuits of optical networks or other communication networks, and diskdriver circuits. The consumer electronic products can include, but arenot limited to, a mobile phone, a telephone, a television, a computermonitor, a computer, a hand-held computer, a personal digital assistant(PDA), a microwave, a refrigerator, an automobile, a stereo system, acassette recorder or player, a DVD player, a CD player, a VCR, an MP3player, a radio, a camcorder, a camera, a digital camera, a portablememory chip, a washer, a dryer, a washer/dryer, a copier, a facsimilemachine, a scanner, a multi functional peripheral device, a wrist watch,a clock, etc. Further, the electronic devices can include unfinishedproducts.

CONCLUSION

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Likewise, the word “connected”, as generally used herein, refers to twoor more elements that may be either directly connected, or connected byway of one or more intermediate elements. Additionally, the words“herein,” “above,” “below,” and words of similar import, when used inthis application, shall refer to this application as a whole and not toany particular portions of this application. Where the context permits,words in the above Detailed Description using the singular or pluralnumber may also include the plural or singular number respectively. Theword “or” in reference to a list of two or more items, that word coversall of the following interpretations of the word: any of the items inthe list, all of the items in the list, and any combination of the itemsin the list.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “can,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or withoutauthor input or prompting, whether these features, elements and/orstates are included or are to be performed in any particular embodiment.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A mobile device comprising: a power amplifierconfigured to amplify a radio frequency (RF) input signal to generate anRF output signal, the power amplifier configured to receive power from apower amplifier supply voltage; a DC-to-DC converter configured tocontrol a voltage level of the power amplifier supply voltage based on acontrol voltage; an error amplifier configured to adjust the voltagelevel of the power amplifier supply voltage based on an envelope of theRF input signal; a low pass filter configured to low pass filter thepower amplifier supply voltage to generate a filtered voltage; and acomparator configured to generate the control voltage based on comparingthe filtered voltage to a reference voltage.
 2. The mobile device ofclaim 1 wherein the DC-to-DC converter includes a buck converter.
 3. Themobile device of claim 2 wherein an output of the buck converter iselectrically connected to the power amplifier supply voltage via aninductor.
 4. The mobile device of claim 1 wherein the error amplifierincludes an input configured to receive an envelope signal that changesin relation to the envelope of the RF input signal.
 5. The mobile deviceof claim 4 further comprising a transceiver configured to generate theenvelope signal and the RF input signal.
 6. The mobile device of claim 1wherein the error amplifier includes an output that is electricallyconnected to the power amplifier supply voltage via an AC couplingcapacitor.
 7. The mobile device of claim 1 further comprising areference voltage generator configured to generate the referencevoltage, the reference voltage generator configured to receive data thatcontrols a voltage level of the reference voltage over a serialperipheral interface.
 8. A method of envelope tracking in a mobiledevice, the method comprising: amplifying a radio frequency (RF) inputsignal using a power amplifier; providing power to the power amplifierfrom a power amplifier supply voltage; controlling a voltage level ofthe power amplifier supply voltage based on a control voltage using aDC-to-DC converter; adjusting the voltage level of the power amplifiersupply voltage based on an envelope of the RF input signal using anerror amplifier; low pass filtering the power amplifier supply voltageto generate a filtered voltage using a low pass filter; and generatingthe control voltage based on comparing the filtered voltage to areference voltage using a comparator.
 9. The method of claim 8 furthercomprising generating the RF input signal and an envelope signal thatchanges in relation to the envelope of the RF input signal using atransceiver, and providing the envelope signal as an input to the erroramplifier.
 10. The method of claim 8 wherein adjusting the voltage levelof the power amplifier supply voltage based on the envelope of the RFinput signal using the error amplifier includes providing an errorcurrent from an output of the error amplifier to the power amplifiersupply voltage via an AC coupling capacitor.
 11. The method of claim 8further comprising receiving data over a serial peripheral interface,and controlling a voltage level of the reference voltage based on thedata using a reference voltage generator.
 12. The method of claim 8further comprising generating the reference voltage using a referencevoltage generator, and dynamically changing a voltage level of thereference voltage between transmission slots of the power amplifier. 13.A phone board comprising: a power management integrated circuit (PMIC)including a DC-to-DC converter configured to control a voltage level ofa power amplifier supply voltage based on a control voltage; and a poweramplifier module including a power amplifier that provides amplificationto a radio frequency (RF) input signal and that receives power from thepower amplifier supply voltage, the power amplifier module furtherincluding an error amplifier configured to adjust the voltage level ofthe power amplifier supply voltage based on an envelope of the RF inputsignal, a low pass filter configured to low pass filter the poweramplifier supply voltage to generate a filtered voltage, and acomparator configured to generate the control voltage based on comparingthe filtered voltage to a reference voltage.
 14. The phone board ofclaim 13 wherein the DC-to-DC converter includes a buck converter. 15.The phone board of claim 14 wherein the power amplifier module furtherincludes an inductor, the buck converter including an output that iselectrically connected to the power amplifier supply voltage via theinductor.
 16. The phone board of claim 13 wherein the error amplifierincludes an input configured to receive an envelope signal that changesin relation to the envelope of the RF input signal.
 17. The phone boardof claim 16 further including a transceiver integrated circuit (IC)configured to generate the RF input signal and the envelope signal. 18.The phone board of claim 13 wherein the power amplifier module furtherincludes an AC coupling capacitor, the error amplifier including anoutput that is electrically connected to the power amplifier supplyvoltage via the AC coupling capacitor.
 19. The phone board of claim 13wherein the power amplifier module further includes a reference voltagegenerator that generates the reference voltage.
 20. The phone board ofclaim 19 wherein the power amplifier module further includes a serialperipheral interface that is electrically connected to the referencevoltage generator, the serial peripheral interface configured to receivedata that controls a voltage level of the reference voltage.